计算采样图像时InputStream读取两次？

Question

我试图采用一种方法来防止从互联网位图读取时发生outOfMemoryError。 我使用对吗？ 流不是从互联网读取两次吗？

BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
URL url = new URL(imageUrl);
InputStream inputStream = url.openConnection().getInputStream();
BitmapFactory.decodeStream(inputStream, null, options);

// Calculate inSampleSize
int coverDimensions = CommonTasks.getDisplayMinSize(getActivity());
options.inSampleSize = calculateInSampleSize(options, coverDimensions, coverDimensions);

 // Decode bitmap with inSampleSize set
options.inJustDecodeBounds = false;
return BitmapFactory.decodeStream(inputStream, null, options);

private int calculateInSampleSize(BitmapFactory.Options options, int reqWidth, int reqHeight) {
        // Raw height and width of image
        final int height = options.outHeight;
        final int width = options.outWidth;
        int inSampleSize = 1;

        if (height > reqHeight || width > reqWidth) {
            final int halfHeight = height / 2;
            final int halfWidth = width / 2;

            // Calculate the largest inSampleSize value that is a power of 2 and keeps both
            // height and width larger than the requested height and width.
            while ((halfHeight / inSampleSize) > reqHeight
                    && (halfWidth / inSampleSize) > reqWidth) {
                inSampleSize *= 2;
            }
        }

        return inSampleSize;
    }

Answer 1

在while使用|| 保持宽度和高度都没有限制。 不 ，您不能重新读取InputStream。

号理论上你可以使用reset() ，但互联网是顺序I / O：

boolen canReset = inputStream.markSupported();
if (canReset) {
    inputStream.mark(Integer.MAX_VALUE);
}
... first read
if (canReset) {
    inputStream.reset();
}
... second read

代替布尔标志，在重置时捕获IOException会更容易：例如，当超出读取限制时，可能会抛出该异常。

只需重新阅读即可。 第二次可能来自缓存。